The present invention relates generally to battery powered lights, such as flashlights and, more particularly, to a light that uses a light emitting diode (LED) powered by a single battery.
Generally speaking, various types of battery powered lights, such as small or miniature flashlights commonly known as pen-lights, exist. One particularly well-known miniature flashlight is sold under the trade name of Mag Light. Miniature flashlights are typically used in applications where a light-weight flashlight having a relatively small profile is desirable, such as in camping, backpacking, hiking, etc. applications. However, miniature flashlights can also be used in other applications, such as in the home, in cars, in boats, in offices such as in doctors"" and dentists"" offices, etc.
Some known miniature flashlights, such as the Mag Light, use a single AAA battery (1.5 volts DC) to drive an incandescent bulb. Unfortunately, the incandescent bulbs of such flashlights are usually very intolerant to rough usage and shocks and, therefore, wear out relatively quickly, requiring frequent replacement. Because locating and buying replacement bulbs for these flashlights is often inconvenient, an owner is likely to throw the flashlight away and obtain a new one rather than go through the trouble of finding and purchasing a new bulb. This is wasteful and can be expensive. Moreover, incandescent bulbs use a lot of power, which drains the battery of these flashlights rather quickly. For example, in a flashlight having a single AA battery driving an incandescent bulb, the battery has a use-life of about eight hours. As a result, the battery of these flashlights needs to be replaced fairly often.
To alleviate the problems with incandescent bulbs, some miniature flashlights use a light emitting diode (LED) as a light source. LEDs, which are solid state devices, typically have a long life and are very tolerant to rough usage and shocks. As a result, the LEDs of these flashlights tend not to need replacement. Furthermore, because LEDs typically only draw a minimum amount of current, they are a more efficient source of light than an incandescent bulb. This, in turn, means that a flashlight using an LED as a light source generally has a longer use-life per battery.
Unfortunately, to be turned on, LEDs typically require a power source that provides 2.4 volts or higher. As a result, a single standard AA or AAA battery, which only provides 1.5 volts DC, will not drive an LED in a standard flashlight device. As a result, in the past, LED flashlights have been made using two or more AA or AAA batteries connected in series as a power source. These additional batteries, of course, increase the size and weight of the flashlight over a miniature flashlight that uses only a single battery, which is undesirable. Still further, other LED flashlights use one or more small specialty batteries that provide a higher DC voltage, such as lithium batteries or other miniature watch or camera batteries. While enabling the manufacture of a small and lightweight flashlight able to use an LED as a light source, these specialty batteries are generally much more expensive and are much harder to find and buy than standard batteries, such as AA or AAA batteries. Replacing the batteries in these flashlights becomes much more expensive and difficult because the user has to go to a specialty store like a watch store or a camera store to find these batteries, which is inconvenient.
A light, such as a miniature flashlight, uses a standard battery, for example, a single AA or AAA battery, to drive a solid state light source, such an LED, even though the DC voltage output of the battery is lower than the turn-on threshold voltage of the solid state device. In one embodiment, a flashlight includes a battery holder electrically connected to a voltage step-up circuit which, in turn, is electrically connected to an LED. The voltage step-up circuit steps up the voltage provided by the battery to a voltage that is above the turn-on threshold of the LED, thereby turning the LED on and causing illumination. The voltage step-up circuit may include an inductor as an energy storage device connected to the LED and to a switch, such as a transistor. In this embodiment, toggling operation of the switch causes the inductor to alternatively store energy and to then discharge energy so that, when discharging energy, the inductor causes the voltage across the LED to be higher than the turn-on threshold voltage of the LED. Thus, in this embodiment, the inductor and switch combination creates an AC voltage across the LED causing the LED to turn on and off at a frequency at which it appears to the user that the LED remains on constantly.
In another embodiment, a light uses a power switching circuit to enable an LED to be driven by a single standard battery which does not provide a DC voltage output large enough to drive the LED unaided. Because the light includes an LED driven by a single battery of a standard size, such as a AA battery, the light can be light-weight and small in size and yet attain the longer life and durability advantages of using an LED as a light source. For example, one embodiment of a flashlight described herein that uses a single AA battery to drive an LED provides a battery life of about 40 hours, as compared to the typical eight hour life for a single AA battery flashlight that uses an incandescent bulb. Still further, the LED of the light described herein can be guaranteed for life because the LED does not burn out easily, as is the case with incandescent bulbs.